FIG. 1 illustrates the functional diagram of a secure terminal TS, specifically banking, according to the previous design.
Such a terminal incorporates a group of functions, such as:                a central processing unit 1 (micro-controller),        a keypad 2,        a volatile memory 3,        a non-volatile memory 4,        a display 5,        a printer 6,        an external connection interface 7,        a magnetic card reader 8 and/or chip card reader 9,        a means of connection to a telecommunication network 10, and        a power supply unit 11 as energy (battery and/or mains).        
These components are connected by a bus group 12 of different natures (power supply, memory, control) and are well known to the man skilled in the art. The whole is based on one or more printed circuits distributed in one or more boxes.
Implementation of this type of terminal is conventional other than that certain security elements must be added in order to proscribe all manipulations capable of altering or extracting financial information (personal identification number PIN, banking transactions, medical files, etc.).
For technical, financial and security reasons, the central unit (micro-controller), memories and certain peripherals for the input/output of sensitive data are confined to the same box. This box has an intrusion detector in order to guarantee the security of said box. Security remains principally physical for this type of solution.
In a more sophisticated embodiment, sensitive data, which moves via the buses and between the functional units, is encrypted. This mode is generally restricted to the central unit, which encodes this data [before sending it] to remote memories or assemblies via the modem.
Different configurations are possible.
A first configuration is a monolithic assembly, in which all the functional sub-assemblies are combined into a single box.
A second configuration is a bi-module assembly, in which the functional sub-assemblies are combined in two boxes according to two combinations. According to the first combination, all the sub-assemblies except the printer and the principal power supply are combined in a first box, and the printer and the power supply (for example the mains) are combined in a second box. According to the second combination, all the sub-assemblies except the principal power supply unit are combined in a first box, and the principal power supply unit (for example the mains) is found in a second box.
Only the second box, which contains the central unit and the peripherals for the input/output of sensitive data, is protected against intrusions.
Traditional solutions impose a global protection of the box and connect functions of different intellectual values. Thus, noble functions that are grouped around the central unit (memories and applications) are de facto connected to the same scale of value as the box that contains them.